So most themes usually access the excerpt using get_the_excerpt() or something similar (which constructs and excerpt if one hasn’t been entered), but for some reason, your theme author decided to use get_the_content() and trim the full content himself instead! Since you add social buttons to the top of your content, your theme strips the html, but the twitter button also contains some text (the word “Tweet”), so that gets left behind.

It’s always better for authors to use standard WordPress functions and methods, or you get weird behavior like this.

I had contacted the plugin author and he advised me to un-check the Apply Content filters in your Advanced settings and that fixed it, but I am not sure if that affects my site in other ways or not, but just wanted to tell you about it.

WordPress allows plugins and themes to hook into various filters, which are then used by WordPress to expand shortcodes, etc. WordPress generally calls a filter (like ‘the_content’) once to expand text for the webpage. As a consequence, some authors mistakenly assume that a filter they have created will only be executed once. WordPress filters are available to any theme and/or plugin that needs to expand text (title, excerpt, content, etc.), which NGFB Open Graph+ uses to provide a complete and accurate meta tag description (as an example).